The aim of the proposed research is to investigate the carrier mediated facilitated diffusion transport of testosterone and glucose through the blood-testis barrier into the seminiferous tubules of the testis, to evaluate the specificity and kinetics of these transport mechanisms and to study the effects of various physiological and endocrinological factors. Carrier mechanisms for other substances e.g. amino acids and nucleosides will also be sought. The significance of the function of the barrier and these transport systems in the control of meiosis will be examined.